1. Field of the Invention
The present invention relates to a blood-pressure monitoring apparatus for use in dialysis that continuously monitors change of blood pressure of a patient during a dialysis treatment, and to a dialyzing apparatus including the blood-pressure monitoring apparatus.
2. Related Art Statement
Since blood pressure of a patient who is undergoing a dialysis treatment may largely lower, there is a need to monitor the blood pressure. A blood-pressure measuring method using a cuff is preferable with respect to reliability. However, when the cuff is used to measure the blood pressure, it is needed to increase a pressure in the cuff up to a value higher than a systolic blood pressure of the patient. Thus, the patient feels discomfort, and accordingly blood-pressure measuring operations each using the cuff cannot be carried out so frequently.
Hence, there has been proposed a blood-pressure monitoring apparatus which successively obtains a piece of blood-pressure-related information that is related to blood pressure of a patient, successively determines an estimated blood pressure of the patient based each piece of blood-pressure-related information, and monitors, based on change of each estimated blood pressure, blood pressure of the patient who is undergoing a dialysis treatment. This blood-pressure monitoring apparatus is disclosed in, e.g., Japanese patent document No. 10-043147 or its corresponding U.S. Pat. No. 5,752,920. The monitoring apparatus iteratively determines an estimated blood pressure based on a pulse-wave propagation velocity at which a pulse wave propagates in patient""s body. If change of the estimated blood pressure is greater than a prescribed threshold value, indicating that patient""s blood pressure may be abnormal, then the monitoring apparatus carries out a blood-pressure measuring operation using a cuff to obtain a more reliable blood-pressure value of the patient.
During a dialysis treatment, blood pressure of a patient that is clinically normal may lower little by little as time elapses. Therefore, it is a conventional practice that when the above-indicated blood-pressure monitoring apparatus is used to monitor blood pressure of a patient during a dialysis treatment, a considerably great threshold value is employed in judging whether change of each estimated blood-pressure value is abnormal, so that a normal time-wise blood-pressure decrease may not be judged as abnormal. However, if the threshold value is too great, the monitoring apparatus cannot quickly find an abnormal blood-pressure decrease.
Thus, it is desirable that the above-indicated threshold value be as small as possible so long as the threshold value does not allow a normal blood-pressure decrease to be judged as abnormal. However, a normal amount of decreasing of blood pressure during a dialysis treatment depends on each individual patient, and an abnormal blood-pressure decreasing amount that needs an emergency treatment also depends on each patient. Thus, the conventional blood-pressure monitoring apparatus has the problems that a normal blood-pressure decrease for a patient may be judged as abnormal and that an abnormal blood-pressure decrease for another patient may not be quickly found. If the abnormal blood-pressure decrease is not quickly found, then the patient may loose his or her life. Therefore, there is a tendency that the threshold value is set at a considerably small value. Thus, normal blood-pressure decreases for a patient may be frequently judged as abnormal, and blood-pressure measuring operations each using a cuff may be carried out on the patient. That is, the patient may be forced to feel unnecessary discomfort.
Meanwhile, a conventional dialyzing apparatus is used such that when the blood-pressure monitoring apparatus generates an alarm sound indicative of the abnormal blood-pressure decrease, a doctor or a nurse hurries to lower a speed of operation of the dialyzing apparatus or temporarily stop the operation of the same. Thus, a considerably long time is taken to conduct an appropriate action to treat the abnormal blood-pressure decrease.
It is therefore an object of the present invention to provide a blood-pressure monitoring apparatus for use in dialysis that can quickly find an abnormal decrease of blood pressure of a patient without erroneously judging a normal blood-pressure decrease as being abnormal, and provide a dialyzing apparatus which can enable, when the abnormal blood-pressure decrease is found, the blood pressure of the patient to be quickly recovered.
The Inventor has carried out extensive studies to achieve the above-indicated objects, and found the facts that although a pattern of change of blood pressure during a dialysis treatment depends on each individual patient, blood pressure of each patient follows a substantially same pattern during each dialysis treatment and that the blood pressure of each patient tends to abnormally lower during only a particular period or periods within an entire duration of each dialysis treatment. Therefore, if a tight threshold value is used to find a blood-pressure abnormality during the particular period of each dialysis treatment, an abnormal blood-pressure decrease can be quickly found and, if a loose threshold value is used to find an abnormality during the remaining periods of each dialysis treatment, a normal blood-pressure decrease is not erroneously judged as abnormal.
As described above, blood pressure of each patient follows a substantially same pattern of change during each dialysis treatment. Therefore, if a time-wise change of blood-pressure values of each patient during each dialysis treatment is stored in a memory device and the blood-pressure values (or the change of the blood-pressure values) stored in the memory device are compared with actual blood-pressure values (or change of the actual blood-pressure values) obtained during each dialysis treatment, only an abnormal blood-pressure change can be monitored during each dialysis treatment and accordingly an abnormal blood-pressure decrease can be quickly found without erroneously judging a normal blood-pressure change as abnormal. The present inventions have been developed based on these findings.
The above objects have been achieved by the present invention. According to a first feature of the present invention, there is provided a blood-pressure monitoring apparatus for use with a dialyzing device, comprising a blood-pressure-related-information obtaining device which iteratively obtains, from a patient who is undergoing a dialysis operation of the dialyzing device, a piece of blood-pressure-related information that can change in relation with a blood pressure of the patient; a change-value determining means for determining a change value representing a change of each piece of blood-pressure-related information iteratively obtained by the blood-pressure-related-information obtaining device; a memory device which stores, for the patient, a plurality of prescribed threshold values corresponding to a plurality of prescribed periods of an entire duration of the dialysis operation, wherein at least one of the threshold values that corresponds to at least one of the prescribed periods is smaller than the other threshold values, and wherein the blood pressure of the patient is more likely to lower during the at least one period of the entire duration, than during the other periods of the entire duration; and a judging means for judging that the blood pressure of the patient is abnormal, when the change value determined by the change-value determining means is greater than one of the threshold values that corresponds to one of the prescribed periods that includes a dialysis time, measured from a commencement of the dialysis operation, when the each piece of blood-pressure-related information is obtained by the blood-pressure-related-information obtaining device.
According to this invention, the change-value determining means determines a change value representing a change of each piece of blood-pressure-related information iteratively obtained by the blood-pressure-related-information obtaining device, and the judging means may find a blood-pressure abnormality, even if a smaller change value may be determined during a period of the entire duration in which the blood pressure of the patient is more likely to lower, than a change value determined during the other periods of the entire duration. In other words, during a period in which the blood pressure is less likely to lower, a greater change value may not be judged as abnormal, than a change value determined during a period in which the blood pressure is more likely to lower. Thus, an abnormal blood-pressure decrease can be quickly found without erroneously judging a normal blood-pressure decrease as abnormal.
According to a second feature of the present invention, there is provided a blood-pressure monitoring apparatus for use with a dialyzing device, comprising a blood-pressure-related-information obtaining device which iteratively obtains, from a patient who is undergoing a dialysis operation of the dialyzing device, a piece of blood-pressure-related information that can change in relation with a blood pressure of the patient; a memory device which stores a normal relationship between blood-pressure-related information and dialysis time; and a judging means for judging that the blood pressure of the patient is abnormal, when a comparison value is greater than a prescribed threshold value, the comparison value being obtained from each piece of blood-pressure-related information iteratively obtained by the blood-pressure-related-information obtaining device, with a piece of blood-pressure-related information, represented by the normal relationship stored in the memory device, that corresponds to a dialysis time, measured from a commencement of the dialysis operation, when the each piece of blood-pressure-related information is obtained by the blood-pressure-related-information obtaining device.
According to this invention, the memory device may store a normal relationship between blood-pressure-related information and dialysis time that is particularly appropriate for each individual patient. This normal relationship represents a normal change of blood pressure of the patient during each dialysis treatment. The judging means obtains a comparison value from each piece of blood-pressure-related information iteratively obtained by the blood-pressure-related-information obtaining device, and a piece of blood-pressure-related information, represented by the normal relationship stored in the memory device, that corresponds to a dialysis time when the each piece of blood-pressure-related information is obtained, and finds a blood-pressure abnormality of the patient based on the thus obtained comparison value. Thus, the present apparatus finds a blood-pressure abnormality based on only an abnormal blood-pressure change, and accordingly can quickly find an abnormal blood-pressure decrease without erroneously judging a normal blood-pressure decrease as abnormal.
According to a third feature of the present invention that includes the second feature (2), the judging means comprises a comparison-value determining means for determining the comparison value by comparing the each piece of blood-pressure-related information obtained by the blood-pressure-related-information obtaining device, with the piece of blood-pressure-related information, represented by the normal relationship stored in the memory device, that corresponds to the dialysis time when the each piece of blood-pressure-related information is obtained by the blood-pressure-related-information obtaining device.
According to this invention, the judging means finds a blood-pressure abnormality when the comparison value determined by the comparison-value determining means is greater than the prescribed threshold value. The comparison value may represent a difference between a piece of blood-pressure-related information, represented by the normal relationship stored in the memory device for the patient, that corresponds to a dialysis time, and a piece of blood-pressure-related information actually obtained from the patient by the blood-pressure-related-information obtaining device at the dialysis time. This means that the judging means finds a blood-pressure abnormality by comparing the normal relationship for the patient and the piece of blood-pressure-related information actually obtained from the patient, with each other. Thus, the present apparatus finds a blood-pressure abnormality based on only an abnormal blood-pressure change, and accordingly can quickly find an abnormal blood-pressure decrease without erroneously judging a normal blood-pressure decrease as abnormal.
According to a fourth feature of the present invention that includes the second feature (2), the monitoring apparatus further comprises a correcting means for correcting an entirety of the normal relationship stored in the memory device, to a corrected normal relationship, such that a piece of blood-pressure-related information obtained by the blood-pressure-related-information obtaining device at a time of commencement of the dialysis operation is equal to a corrected piece of blood-pressure-related information, represented by the corrected normal relationship, that corresponds to the time of commencement of the dialysis operation, wherein the judging means comprises a comparison-value determining means for determining a comparison value by comparing a piece of blood-pressure-related information obtained by the blood-pressure-related-information obtaining device at a dialysis time measured from the time of commencement of the dialysis operation, with a corrected piece of blood-pressure-related information, represented by the corrected normal relationship, that corresponds to the dialysis time.
Blood pressure of each patient will change in day even if the patient would be healthy. The comparison value determined by the comparison-value determining means in accordance with the third feature (3) does not exclude the normal change of blood pressure of the patient. In contrast, according to the fourth feature (4), the correcting means corrects an entirety of the normal relationship stored for the patient in the memory device, to a corrected normal relationship, such that the piece of blood-pressure-related information actually obtained from the patient by the blood-pressure-related-information obtaining device at the time of commencement of the dialysis operation is equal to the corrected piece of blood-pressure-related information, represented by the corrected normal relationship, that corresponds to the time of commencement of the dialysis operation. This corrected normal relationship does not include the normal change of blood pressure of the patient. The comparison-value determining means determines a comparison value by comparing a piece of blood-pressure-related information obtained by the blood-pressure-related-information obtaining device at a dialysis time, with a corrected piece of blood-pressure-related information, represented by the corrected normal relationship, that corresponds to the dialysis time, and the judging means finds a blood-pressure abnormality based on the thus determined comparison value. Thus, the present apparatus can more quickly find an abnormal blood-pressure decrease without erroneously judging a normal blood-pressure decrease as abnormal.
According to a fifth feature of the present invention, the monitoring apparatus further comprises an actual-change-value determining means for determining an actual change value of each piece of blood-pressure-related information iteratively obtained by the blood-pressure-related-information obtaining device; and a normal-change-value determining means for determining a normal change value by which the blood-pressure-related information, represented by the normal relationship stored in the memory device, changes in a period in which the each piece of blood-pressure-related information has changed by the actual change value determined by the actual-change-value determining means, wherein the judging means obtains the comparison value by comparing the actual change value determined by the actual-change-value determining means, with the normal change value determined by the normal-change-value determining means.
According to this invention, the judging means may find a blood-pressure abnormality, e.g., when a difference between the actual change value and the normal change value is greater than the prescribed threshold value. The actual change value represents an actual change of blood pressure of the patient during the dialysis treatment; and the normal change value represents a normal change of blood pressure of the patient during each dialysis treatment. Therefore, the judging means finds a blood-pressure abnormality by comparing the actual blood-pressure change during the dialysis treatment with the normal blood-pressure change during each dialysis treatment. Thus, the present apparatus finds a blood-pressure abnormality based on only an abnormal blood-pressure change, and accordingly can quickly find an abnormal blood-pressure decrease without erroneously judging a normal blood-pressure decrease as abnormal.
According to a sixth feature of the present invention, the memory device stores, as the normal relationship, an average of a plurality of normal relationships, each between blood-pressure-related information and dialysis time, that have been obtained by the blood-pressure-related-information obtaining device during a plurality of dialysis operations which have been carried out on the patient, and the monitoring apparatus further comprises an updating means for updating the normal relationship stored in the memory device, based on a relationship between blood-pressure-related information and dialysis time that is obtained by the blood-pressure-related-information obtaining device during the dialysis operation, when the judging means does not judge, during the dialysis operation, that the blood pressure of the patient is abnormal.
According to this invention, the updating means updates the normal relationship stored in the memory device, based on a relationship between blood-pressure-related information and dialysis time that is obtained during the current dialysis operation. Thus, the present apparatus can update the normal relationship although the blood pressure of the patient naturally increases as the age of the patient increases. Therefore, the present apparatus can quickly find an abnormal blood-pressure decrease without erroneously judging a normal blood-pressure decrease as abnormal.
According to a seventh feature of the present invention, there is provided a dialyzing apparatus, comprising a dialyzer; a pump which controls an amount of a dialyzing fluid that is supplied to the dialyzer; a blood-pressure monitoring apparatus according to any of the first to sixth features (1) to (6); and a fluid-amount control means for controlling, when the judging means judges that the blood pressure of the patient is abnormal, the pump to decrease the amount of the dialyzing fluid supplied to the dialyzer.
According to this invention, when the judging means finds a blood-pressure abnormality, the fluid-amount control means automatically controls the pump to decrease the amount of the dialyzing fluid supplied to the dialyzer. Thus, the present apparatus can quickly cause the blood pressure of the patient to be recovered.